Texture and Color mixing
You cannot mix a color(or a texture) with a shader in Cycles. You are currently mixing a texture with a Diffuse BSDF shader - that's the problem. It will be enough to disconnect it and set the color directly in the MixRGB node to fix this. 

If you wanted to have a separate node for the color for some reason(for example if you want to connect it to multiple inputs so you can change them all at once), you can use RGB node that you can find among Input nodes.